Historically the use of the MKS system of units succeeded the centimetre–gram–second system of units (CGS) in commerce and engineering. The metre and kilogram system served as the basis for the development of the International System of Units, which now serves as the international standard. Because of this, the standards of the CGS system were gradually replaced with metric standards incorporated from the MKS system. The exact composition of the MKS system changed over time. It incorporated fundamental units other than the metre, kilogram, and second in addition to derived units. An incomplete list of the fundamental and derived units appears below. Since the MKS system of units never had a governing body to rule on a standard definition, the list of units depended on different conventions at different times.
Cycle. (This dimensionless quantity became synonymous with the term "cycle per second" as an abbreviation. This circumstance confused the exact definition of the term cycle. Therefore, the phrase "cycle per metre" became ill-defined. The cycle did not become an SI unit.)